Both studies involved people with nonalcoholic steatohepatitis (NASH), an aggressive disease characterized by fat in the liver. It affects 2 percent to 5 percent of Americans, and can lead to permanent liver damage, according to the study published in the August issue of the journal Gastroenterology.

"While the underlying cause of NASH is unclear, we most commonly see this condition in patients who are middle-aged and overweight or obese," Dr. Giulio Marchesini, of the University of Bologna, Italy, and colleagues wrote in an editorial accompanying the studies.

"These two large prospective cohort studies strengthen the evidence that, no matter how you lose weight, weight loss improves liver health. Both bariatric surgery for morbidly obese patients or lifestyle modifications are viable options," they added.

In one study, researchers in Cuba found that nonalcoholic steatohepatitis was resolved and liver scarring reversed in overweight and obese people who achieved a weight loss of 10 percent or more after one year of lifestyle changes involving a low-calorie diet and exercise.

Weight loss of 7 percent to 10 percent reduced disease severity in some patients, including men and those without diabetes. However, worsening of liver scarring occurred among 93 percent of those with a weight loss of less than 5 percent.

In the other study, researchers in France found that nonalcoholic steatohepatitis disappeared in 85 percent of obese patients one year after they had weight-loss surgery. The success rate was higher among those with mild nonalcoholic steatohepatitis (94 percent) than among those with severe disease (70 percent).